Inverted three-stage Doherty amplifier
An inverted three-stage Doherty amplifier is disclosed. The amplifier provides an input power divider, a carrier amplifier, two peak amplifiers, and an output combiner. The output combiner includes five quarter-wavelength (λ/4) lines, three of which correspond to the three amplifiers, one of which combines an output of the carrier amplifier with an output of the first peak amplifier, and the last of which combines the combined output of the carrier amplifier and the first peak amplifier with an output of the second peak amplifier. The five λ/4 lines have respective impedances to optionally adjust the output impedance of the respective amplifiers.
1. An inverted three-stage Doherty amplifier that outputs an amplified signal by receiving an input signal, comprising:
an input power divider that receives the input signal and outputs three divided signals, where one of the three divided signals has a phase delayed by it π/2 from phases of the rest of the three divided signals;
a carrier amplifier including an offset transmission line, the carrier amplifier receiving one of the rest of the three divided signals;
first and second peak amplifiers each including offset transmission lines, the first peak amplifier receiving another of the rest of the three divided signals, the second peak amplifier receiving the one of the three divided signals, the offset transmission line in the carrier amplifier and the offset transmission lines in the first and second peak amplifiers converting output impedances thereof to be short-circuits when the carrier amplifier and the first and second peak amplifiers are turned off; and
an output combiner that combines outputs of the carrier amplifier and the first and second peak amplifiers, the output combiner including,
a first quarter-wavelength line connected with the carrier amplifier,
a second quarter-wavelength line connected with the first peak amplifier,
a third quarter-wavelength line connected with the second peak amplifier,
a fourth quarter-wavelength line connected with the first quarter-wavelength line and the second quarter-wavelength line, the fourth quarter-wavelength line combining an output of the carrier amplifier provided through the first quarter-wavelength line with an output of the first peak amplifier provided through the second quarter-wavelength line, and
a fifth quarter-wavelength line connected with the third quarter-wavelength line and the fourth quarter-wavelength line, the fifth quarter-wavelength line combining an output of the second peak amplifier provided through the third quarter-wavelength line with a combined output of the carrier amplifier and the first peak amplifier provided through the fourth quarter-wavelength line; and outputting a combined output of the carrier amplifier and the first and second peak amplifiers,
wherein the first peak amplifier has a size greater than a size of the carrier amplifier; and
wherein the second peak amplifier has a size greater than the size of the first peak amplifier.
2. The inverted three-stage Doherty amplifier according to claim 1 ,
wherein the carrier amplifier and the first and second peaking amplifiers have a size ratio of 1:m 1 :m 2 , and
wherein the fourth quarter-wavelength line and the fifth quarter-wavelength line have impedances of (1+m 2 /m 1 )*Z 0 and (1+m 1 /m 2 )*Z 0 , respectively, where Z 0 is an impedance of a load for the inverted three-stage Doherty amplifier.
3. The inverted three-stage Doherty amplifier according to claim 2 , wherein the fifth quarter-wavelength line and the fourth quarter-wavelength line have impedances in a ratio of √2.
4. The inverted three-stage Doherty amplifier according to claim 2 , wherein the carrier amplifier and the first and second peak amplifiers in the respective sizes thereof satisfy a condition of (1+m 1 )=m 2 .
5. An inverted three-stage Doherty amplifier that outputs an amplified signal by receiving an input signal, comprising
an input power divider that receives the input signal and output two divided signals, where one of the two divided signals has a phase delayed by π/2 from the phase of the other of the divided signals;
carrier amplifier including an offset transmission line, the carrier amplifier receiving the other of the divided signal;
first and second peak amplifiers each including offset transmission lines, the first peak amplifier receiving the other of the divided signals, the second peak amplifier receiving the one of the divided signal, the offset transmission line in the carrier amplifier and the offset transmission lines in the first and second peak amplifiers converting output impedances thereof to be short-circuits when the carrier amplifier and the first and second peak amplifiers are turned off; and
an output combiner that combines outputs of the carrier amplifier and the first and second peak amplifiers, the output combiner including,
a first quarter-wavelength line connected with the carrier amplifier,
a second quarter-wavelength line connected with the first peak amplifier,
a third quarter-wavelength line connected with the second peak amplifier,
a fourth quarter wavelength line connected with the first quarter-wavelength line and the second quarter-wavelength line, the fourth quarter-wavelength line combining an output of the carrier amplifier provided through the first quarter-wavelength line with an output of the first peak amplifier provided through the second quarter-wavelength line, and
fifth quarter-wavelength line connected with the third quarter-wavelength line and the fourth quarter-wavelength line, the fifth quarter wavelength line combining an output of the second peak amplifier provided through the third quarter-wavelength line with a combined output of the carrier amplifier and the first peak amplifier provided through the fourth quarter-wavelength line; and outputting a combined output of the carrier amplifier and the first and second peak amplifiers,
wherein the first peak amplifier has a size greater than a size of the carrier amplifier,
wherein the second peak amplifier as a size greater than the size of the first peak amplifier, and
wherein the input power divider includes a 90° hybrid coupler including a transmitter port and a coupled port, the carrier amplifier and the first peak amplifier receiving the another of the divided signals as output from the transmitter port, the second peak amplifier receiving the one of the divided signals as output from the coupled port.